How does nerve damage cause rash on the skin? And what exactly hurts, the nerve damage or the blistery skin?
Also how do antidepressants relive the pain?
In: Biology
During chickenpox infection, it’s thought that the virus moves down the nerve pathway into the main body (neuron) of the nerve cells. It never gets completely cleared from your system and lays there in a latent state. Once you get old or immunocompromised, the virus reactivates and is able to cause the rash you see in shingles. Because it follows the nerve, it causes a rash in the area of the skin that the nerve controls/innervates.
The pain is both because of the blistery skin and because of the nerve involved. The neuropathic or nerve component isn’t treated well with opioids and anti-inflammatories. Specific antidepressants called tricyclics (or other neuropathic pain drugs like pregablin) are used for the pain.
Tricyclics work by reducing reuptake of particular neurotransmitters, allowing them to persist longer in the synapse where neurons communicate between each other. It’s different to how they act in your brain for antidepressant effects. The gist is that it activates existing pathways that your body uses reduce pain.
My brother has shingles twice. He said the pain is mostly in the nerves while the blisters (when open and weeping) sting and hurt like sunburn. In all honesty never heard of antidepressants helping with the pain, my brother was on a strong course of antibiotics, pain relief and lotion for the blisters. He was ill for about 2 months, 3 weeks being the painful shooting pains in his chest.
u/tgpineapple explained the mechanism of Shingles well. As to how to relieve the pain from shingles, there is a little more I would like to add.
The pain from shingles is thought to be related to nerve injury. This leads to what is called neuropathic pain, a pain caused by nerve damage (there is a proportion of the pain caused by injury to the skin directly and possible additional bacterial infections in the area, but we will not discuss that here). For most people, tylenol and NSAIDs (ibuprofen, motrin, aleve, etc) is enough to manage the pain. If that is not enough, then you can consider a short course of steroids or a short course of narcotics (though narcotics are typically not used). Steroids will simply reduce the inflammatory burden along the nerve. Narcotics will mask the pain (again typically not used). Beyond that, you have the option to specifically treat neuropathic pain. The main medication that has been shown to help is gabapentin (neurontin) or pregabalin (lyrica). The way these medications work is a little complicated. The short of it is they limit the ability of nerves to stimulate something (such as when they stimulate the brain in response to pain).
In regards to anti-depressants, they are typically not used when somebody has acute shingles. This means that when someone has the rash and has pain related to it, anti-depressants won’t help. There are a subset of people that develop chronic nerve pain in that area even after the Shingles infection has resolved. In those patients there is consideration for a specific antidepressant that has neuropathic properties. That anti-depressant is duloxetine. Many pain specialists use duloxetine to help manage neuropathic pain. Beyond that, there isn’t a role for anti-depressants in the treatment of pain related to Shingles.
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